Intercommunicating apparatus



R. H. CAMPBELL INTERCOMMUNICATING APPARATUS Dec. 8, 1953 3 Sheets-Sheet 1 Filed May s, 1948 Dec. 8, 1953 R. H. CAMPBELL INTERCOMMUNICATING APPARATUS 3 Sheets-Sheet 2 Filed May 3, 1948 1N VEN T 01?.

62/6 d'ffm/v zzz Dec. 8, 1953 R. H. CAMPBELL INTERCOMMUNICATING APPARATUS 5 Sheets-Sheet 3 Filed May 3, 1948 INVENTOR. at/54M? vzeez BY 79% M (47 Patented Dec. 8, 1953 2,662,115 INTERCOMMUNICATING APPARATUS Richard H. Campbell, Racine, Wis., assignor to Webster Electric Company, Racine, Wis., a corporation of Delaware 1 Application May 3, 1948, Serial No. 24,785

Claims.

The present invention relates to intercom,- municating systems and to apparatus for use in such systems.

One of the objects of the present invention is to provide a new and improved system as well as units for the system including a number of stations or units so constructed and arranged so as to prevent amplifiers at the stations from being cascaded or connected to each other in series, i. e., to prevent what for convenience may be called double amplification.

Another object of the present invention is to provide a new and improved intercommunicating system as well as units for such a system in which a communication. circuit at the calling station is opened in the event a busy station is selected and automatically completed when the busy condition ends.

A further object of the present invention is the provision of a new and improved intercommunicating system and apparatus for use therein wherein double amplification is prevented by means including either a single or two current responsive means, one of which may be a. sen sitive one.

Another object of the present invention is to provide new and improved communication apparatus wherein busy station responsive means is provided to connect electroacoustical translating means to a communication circuit either through a communication direction controlling switch or independently of the switch.

A further object of the presentinvention it to provide a new and improved intercommunieating system including audible busy signal :means.

A still further object of the present invention is to provide a new and improved intercommunicating system including a plurality of stations of a first type including amplifying means and a plurality of stations of a second type having no amplifying means, and wherein the stations of the second type have means for indicating whether or not stations of the first type are busy and also have means for calling stations of the first type.

Other objects and advantages of the present invention will become apparent from the ensuing description of illustrative embodiments thereof, in the course of which reference is had to the accompanying drawings, in which:

Figs. 1 and 2 constitute, when placed alongside each other, a diagrammatic representation of a communicatipn sy t m embodying the 5mvention; and

Figs. 3 and 4. are fragmentary views of modified portions of the apparatus shown in Fig. 1.

Referring now to Figs. 1 and 2, it may be noted that the illustrated system is of the loud-speaking type, wherein communication can be carried on alternately in opposite directions between a plurality of central or master stations under the control of manually operable communication direction control switches thereat; and wherein communication may be carried on between a master station and one or more remote or sub stations under the control of the communication direction control switch at a master station. The master stations are indicated by the reference characters I and 2 and the substations by reference characters 3 and 4.

All the stations provided with electroacoustical translating devices capable of being utilized both as transmitters and receivers, such as the loudspeakers II to 14, inclusive, which may be of the well known permanent magnet type. The master stations are provided with amplifiers l6 and I8 communication direction control switches 2| and 22, and station selector switches indicated generally by reference characters 24 and 26 for selecting other master or substations.

In order to simplify further detailed description of the apparatus at the master stations, the apparatus at but one station will be described and like elements at both will be indicated by like reference characters.

The amplifier (and reference is now had particularly to station I) may be of any Well known construction and has, therefore, not been illustrated in detail. It is believed suflicient to say that it comprises an input transformer 26 and an output transformer 28. Power is supplied to it from a suitable source of alternating current through transformer 30 and in part through a rectifier comprising the tube 32 and energized from the transformer. The filaments of the amplifier tubes are supplied from transformer secondary winding 34, while the rectifier output (the plate voltage supply) is supplied to the tubes under the control of the communication direction control switch 2| (22 at station 2), the arrangement being such that the circuits are completed when the switch is in two of its three positions. These two positions are the talk and listen positions. When the switch is in these positions, the plate circuits are completed through conductor 36, switch blade 38 operable with and physically forming part of the comvmunuication control switch-conductor 40 filter 42, and conductor 44.

switch, the loudspeaker is connected to a communication circuit comprising conductors 4B and 48 adapted to be connected to the interstation circuits through a selector switch .24 and the amplifier is inoperative because switch 38 disconnects the plate voltage supply. In the listion 2 is shown) of the communication control fl .4 station and for preventing connection of the amplifier at the calling station to a busy station. This new and improved means automatically breaks the communication circuit 46, 48, so that the amplifier at the calling station cannot be connected to a called busy station. Thus, it is impossible to connect the amplifiers in series and double amplification is avoided. One of the advantages of breaking the circuit 46, 4B is that neither the amplifier input nor amplifier output can be connected to a called station so that even 'humffrom the amplifier output cannot be placed on the .called station line. A further feature of thepresent invention is that the calling station ten position (in which switch 2-I of station I is shown), the communication circuit 46, 48 is connected to the input of the amplifier and the output of the a plifier is connnected 15. the loudpeaker. .In the talk position, the connections of the circuit and l udp aker to the amplifier r reversed. In boththe talkand listen positio s. th plate voltage upply .is completed, as already desc ibed.

In the idle position of the communication .direc'tion control switch .2], loud-speaker III is connected to the communication circuit '46, 48 through the switch 21 and .a switch blade .50 jorming part of a first current responsive means 52,, forming an important .fea'ture of the present invention. The connection includes conductors .54 and 56 connected to switch'blades 58 and .60 of switch 2.I (in its idle position). Switchblade 69 is connected directly to the communication circuit conductor 48 and switch blade .58 is connected to conductor 46 through conductor 62 and switch blade 50 in its normal position, in which it is shown at both stations ;I and .2. .In this idle position of the communication .direction control switch, the amplifier input circuit which includes conductors 64 and .65 i open. while the amplifier output circuit which includes conductors 58 and 1.0, is shorted by switch blades 12 and 14 of the communication direction control switch through resistors 75 and '18.- hl o, the plate supp y voltage is discontinued because switch .38 is open.

In the listen position of the communication direction control switch, the input of the amplifier is connected to the communication circuit 4.0, through conductors 54, B5, switch blades and 5.8, conductor 43, and conductor 62, and switch blade 50. The amplifier output is conne ted to loud-speaker ll through conductors 88 and T10, the switch blades I2, l3, l4 and 80, 82

of he communication direction control switch, resistors 16 and 18, and conductors .54 and 5.6.. It should be noted that resistor 18 is in series with the loud-speaker, whereas resistor 16 is in parallel with it.

In the talk position of the communication diection control switch, the loudspeaker is connected to the input and the communication circult to the output of the amplifier. The inp of the amplifier is connected to the loudspeaker through conductors 66 and 54, switch blades 80, 82 and 12, 74, and conductors 54 and .56.. The output is connected to circuit 46, 48 through conductors 68 and 10 and switch blades 58 and 60, which are connected to conductors 6.2 and 48 and thus to the communication circuit.

One of the primary features or the present invention resides in the provision of new and improved means for indicating whether or not a selected station is busy at a calling or selecting amplifier is reconnected to the communication circuit automatically when the calling station is no longer busy.

In .the embodiment of the invention illustrated in "Figs. 1 and 2, two current responsive means are utilized, whereas in the embodiments of Figs. 3 and 4;,bu't asingle current responsive means is used. Of the two current responsive means in the system of Figs. 1 and .2, the first, which has been indicated by reference character 52, operates a number ofswitches and is'controlled by a second, indicated by reference character 90, which is a more'sensitive device.

The current responsive means of relay 90 is normally energized whenever the apparatus is in operation, as *it "is whenever the power supply switch 3| is closed to energize the transformer 30. When this is done, the relay winding 92 is connected across the plate voltage supply through conductor '36, the series connected resistors 94 and 96 and the ground connection 98. A filter condenser I00is connected across ground and the junction of the two resistors.

The relay .90 energizes the winding I02 of relay 52 in its energized or operated position. At this time the winding I02 is connected across the plate voltage supply through conductor 36, the

series connected resistors I04 and I06, and conductor I08 leading to one terminal of the winding, the other terminal of which is connected to ground through conductor H0, switch blade H2 of relay 0.0, and ground connection 98. A filter condenser H4 is connected between ground and the junction of resistors 1.04 and I06.

The arrangement of the current responsive means is such that if a busy station is selected with the communication direction control switch in its uppermost or idle position, which is also its selecting position, the relays 9i) and 52 are deenergized and remain deenergized as long as the selected station is busy and even though the communication direction control switch be moved from its selecting to its talk or listen positions. When the relays are deenergized, the communication circuit 46, 48 is broken so that the amplifier cannot be connected to it, and the loudspeaker is preferably kept connected to the coinmunication circuit so that the calling station can listen to the communication between the busy stations. Also, visual and audible signals are operated at the calling station.

The current responsive means are connected to the communication circuit in the idle position of the communication direction control switch through conductor I20, switch blade I22 in its uppermost position, conductor I24, switch blade I28 forming part of the relay 5.2, conductor I28, and the resistors I30 and I32 connected across circuit 46, 48 and to the junction of which conductor I20 is connected.

The relay is deenergized when a busy staconnection I34.

station, the communication circuit tion. is selected by connection thereof to ground so that the current flow through it is decreased to a point where it no longer remains in its operated position. The grounding is effected through the called busy station at which the circuit 45, 43 and, therefore, the interstation used at any particular time, is grounded through the witch I22 in its talk or listen positions, whereat it connects the communication circuit to ground through the previously referred to circuit ineluding switch I26, conductor I24, and the ground The connection of the circuit 48, 38 to ground is illustrated in Fig. l, in which the communication direction control switch is illustrated in its listen position.

When the current responsive means are deenergized in response to the selection of a busy 5- 5, 48 is broken, the loud-speaker is connected to the communication circuit independently of the communication direction controlling switch, the relays are connected to the communication circuit independently of the communication direction control switch, and visual and audible signals are operate The communication circuit 4-5, E3 is broken by switch 59, which is connected to conductor 48. When operated, the switch 53 also connects the loud-speaker to the circuit 46, 58 through conductor I35 so that the speaker remains connected to circuit d8, d8 as it was in the idle or selecting position.

The current responsive means are connected to the communication circuit independently of switch 2i through conductor 38, the switch blade 525 in its uppermost position, conductor 28, and resistors I39 and I 32.

The visual indication is provided by the deenergization of a normally lighted pilot light l ill. The light is normally connected across a portion of the secondary winding t l through a circu't including conductor Hi2, conductor and a third switch blade E li of relay 52, which is con-- nected to ground. When the relay 52 is doenergized upon the selection of a busy station, the switch I 36 moves to its other position to deenergize the light i lil and to complete an energluing circuit for a buzzer i-"lll which is connected across another portion of secondary winding 34 through conductor lei The switch blades i26 and 5% are of the shorting type, i. e., they make before break.

The system embodying the present invention may include a number of central or master stations, although but two have been illustrated. The stations are interconnected by a plurality of interstation circuits, and each station is preferably connected to an interstation circuit inividual to it. Thus, station 5 is connected to an interstation circuit IiiI individual o it by a normally closed station selector switch 24-I. Station 2 is connected to its individual interstation circuit 562 by the selector switch 26-2. Stat-ion i has a selector switch 2l2 for selecting station 2, and station 2 has a selector switch 22--i for selecting station E. If more stations are used, more station sel ctor switches and interstation circuits are provided.

The system illustrated in Figs. 1 and 2 also includes the two substations 3 and i. Station 3 is shown arranged so that it can be called from station 3, and station 4 is arranged so that it can be called from station 2. The interstation circuits individual to stations 3 and d are in- .jdicatedby referenceoharacters N3 and I64, re.-

the circuit 46, 48.

spectively, and circuits tothem can be completed through the selector switches 24-3 and 26-4.

The remote stations can also call the master stations and they are provided with means for indicating whether or not the called master station is busy. Thus, each of the substations in cludes a two-position switch It? normally connecting the loud-speaker to its associated interstation circuit and operable to connect the loudspeaker to a "call-in line I66 leading to the master station and used for signalling and, if desired, for communication. When the call-in line is used for communication, it is connected to communication circuit 46, 48 by switch I68 at the central station. When this switch is closed, relay 52 is permanently energized through the resistors I84 and I06 and a ground connection completed through conductor I'Ifl, switch blade I "I2 operable simultaneously with the switch I59, and conductor Il l. The call-in line conductors are joined by the series connected resistors HE and N3, the junction of which is connected by conductor ISO to conductor I24, which, it may be remembered, is connected to the plate voltage supply when the communication direction control switch is in its idle position. The substa tion circuit has the series connected resistors I32 and I34 connected across it and the junction of these may be connected to ground through conductor I88, switch blade I88 operable with switch I65, and the meter Idil, which may be a low resistance meter.

The operation of the system illustrated in Figs. 1 and 2 will now be reviewed as a. whole. In this description, it is assumed that the power switches SI at the master stations I and 2 are closed, thus placing the apparatus in operation. The relays 52 and 9B are energized with the result that switch blades 56, I26 and I46 are in their indicated positions. The pilot lights I40 are energized through circuits including switch blades I48. The communication circuits 46, 48 are completed through switch blades 59 and switch blades 1'26 connect the communication circuits to the switch blades I22.

It is assumed further that stations I and 3 are communicating with each other, as shown in Fig. 1. For example, it can be assumed that station I called station 3. This can be done by closure of the selector switch 24-3 at station I connecting circuit I63 individual to station 3 to In the indicated position of the communication direction control switch 2|, the loud-speaker I3 is connected to the input of amplifier I6 and loud-speaker II to the output through circuits previously described in detail. The plate voltage supply is completed through switch blade 38 so that communication can be carried on between stations I and 3 under the control of the communication direction control switch 2| at station I.

When station I is conditioned for communication with another station, the communication circuit 45, 48, and thus all interstation circuits connected thereto, in this case circuits I6I and I63, are connected to ground through switch blade I26 of relay 52 and switch blade I22 of switch 2I. If another station, such as station 2, selects station I, the communication circuit at station 2 will be broken and the busy signals thereat operated. I

Assume now that station 2 selects station I when the latter is busy. The selection is made with the switch 22 in its indicated idle or select-- ing position. In this position, the relay 2 connected to .the station Icomniunication circuit 46, 48 through :switch blades I22 and I26. Then, when the selection is actually made by .the closure of selector switch 26-'-I, the high potential end of relay 90 is connected to ground through the circuit including the interstation circuit IBI, the circuit 46, 48 at station I and switch blades I26 and I22 at station I. As a result, the energization of relay 90 is reduced to a value such that it is released or returned to nonoperated position. Switch I I2 of the relay thus opens and deenergizes relay winding I02 and the switch blades 50, I26 and I46 of the relay are returned, as by a spring, to their other positions. Circuit 46, 48 is broken by switch 50 and the relay 80 is connected by switch blade I26 and conductors I38 and I28 to the circuit 46, 48, thereby to prevent operation of relay 90 even though the circuit through switch blade I22 be broken by operation of the switch 22 to its talk or listen positions. The pilot light I40 is deenergized and the buzzer I48 energized by-switch blade I46. The loudspeaker I2 remains connected to the interstation circuit through switch blade 50 so that the operator at station 2 can listen in on the busy line.

The amplifier cannot be connected to the interstation circuit as long as station I remains busy, because of the opening of circuit 46 by switch 50. Thus, double amplification is prevented. Furthermore, the arrangement is such that the communication circuit is automatically reclosed as soon as station I is no longer busy, and this is true no mattt er what position the switch 22 is left in. When station I is no longer busy, i. e., the switch 2| is returned to its idle position, then the ground is removed from the interstation circuit and relay 90 is energized and operates to close switch II2. Relay 52 immediately operates to return to its indicated position, thus apprising the operator at station 2 that station I is no longer busy.

A substation can also call a master station, as will now be reviewed in connection with a call from station 4 to station 2. To make the call, the switches I65 and I88 are operated to connect the meter I90 to circuit I66, which is connected through conductors I80, I24, switch I22, and conductor I20 to the plate voltage supply at station 2. As a consequence, the meter gives a reading and indicates that station 2 is not busy. At the same time the relay 90 is grounded through the meter, which is of low resistance, with the result that relay 52 is deenergized and the light I40 deenergized and the buzzer I48 is operated to give both visual and audible indications that station 2 is being called from a substation. To answer the call, the switch I68 is closed. The switch H2 is closed simultaneously to reconnect winding I02 of relay 52 to the plate voltage supply, thereby to complete the communication circuit so that the switch 22 can be operated to effect communication with station 4. The communication can be carried on through switch I65 in its displaced position and with switch I68 closed or the operator at station 2 can ascertain which substation is calling and thereafter close the corresponding station selector switch 26 and open switch I68, after which communication can be carried on just as though the master station had originated the call.

In the event station 2 is busy when station 4 calls it, the switch I22 is connected to ground so that when switches I65 and I88 at station 4 are closed, the meter I gives no reading.

There is thus provided an indication at station 4 that station 2 is busy.

Fig. 3 illustrates in fragmentary form a modified apparatus at a central station. The main difference between the apparatus of Fig. 3 and that described above at stations I and 2 is that but a single relay I 02 is utilized. It operates the switches 50, I26 and I46, as before, but instead of being controlled by a relay corresponding to the relay it is connected to the plate voltage supply by a conductor 200 and the ground connection 202. The resistors 94 and 96' correspond generally to the resistors 94 and 06 except that they may have lower values, for example, of about 24,000 ohms each, as compared with 62,000 ohms each for the previously described resistors. The relay windings I02 and I02 may both have resistances in the neighborhood of 10,000 ohms. The embodiment of Fig. 3 does not include any substations and, therefore, the switches I68 and H2 and the interstation circuit I66 have not been shown. Also, the audible signal means I48 has been omitted.

The operation of a system including a number of stations like the one illustrated in Fig. 3 is similar to that described above in connection with Figs. 1 and 2, except that the relay winding I 02 is connected to the communication circuit and operates the switches 50, I26 and I46. In other words, one relay takes the place of two.

The embodiment of Fig. 4 is similar to that of Fig. 3 in that one relay winding I02 is used, but differs from it in the connection of that winding to the communication circuit and to the communication direction control switch I22. The switches 50 and I46 are connected and operate as in Fig. 3.

The relay winding I02 is connected to the communication circuit in the idle position of the switch 2I through the switch blade I22, the connection being effected through conductors 2I0, 2I2, switch blade I 22 in its uppermost or idle position, conductor 2I4, and the resistors I30 and I32. When a busy station is selected, the winding I02 is connected to ground, as before, with the result that the switch blades 50, I26 and I46 are returned to their nonoperated positions. As long as switch 2| remains in its idle position, the relay winding I02 remains connected to the communication circuit 46, 48, as previously described. If the switch is operated to its listen or talk positions, then the relay winding I02 is connected to the communication circuit through conductor 2| 0, switch blade I26, conductor 2I6, switch blade I22 (now in its indicated position), and conductor 2I4. As a result, the relay winding I02 remains nonoperated no matter what the position of switch 2i, as long as the station is connected to a busy station.

While the present invention has been described in connection with the details of three illustrative embodiments thereof, it should be understood that these details are not intended to be limitative of the invention, except in so far as set forth in the accompanying claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

1. An intercommunicating system including a plurality of stations, interstation circuits connecting said stations, amplifying means having an input and an output and a plural position communication direction controlling switch means and a two way communication circuit, and amplifying means input and. output circuits; controlled by it at each station for completing the connections of said interstation circuits to the input and output of said amplifying means in a plurality of positions of said switch means; circuit means at each station associated with its said switch means for placing its interstation circuit in one of a plurality of current conducting busy condition when the station is communicating with another, each of said communication direction controlling switches being operable also to a further station selecting position, and means including said switch means in said selecting position and current responsive means at each station controlled in response to the busy condition of a selected interstation circuit for breaking said controlled circuit when said busy condition obtains and for completing said circuit when said busy condition ends.

2. In a multiple station intercommunicating system, the combination including, means including interstation communication circuits, an electroacoustical translating device, a multiposition communication controlling switch 'means and an amplifier having input and output connections at each station controlled by the switch means thereat enabling the device to be connected to a circuit or the amplifier input or out put and the circuit to the amplifier output or input, respectively, for establishing communication circuits between stations, each station including also normally closed switch means in the circuit between said communication controlling switch means and interstation circuits, a first current responsive means, means operably connecting said first current responsive means to said normally closed switch means and operable to open the latter, a second current responsive means and circuits controlled thereby for controlling the energization of said first current responsive means, means including a switch controlled by said communication controlling switch means for connecting said second current responsive means to a communication circuit when said switch means connects the device to a communication circuit, means including switch means operable by said communication controlling switch means for grounding the interstation communication circuit when said device is connected to said amplifier, whereby the second current responsive means at a station selecting another station whereat the device is connected to the amplifier is grounded and operated to operate the first current responsive means to open said normally closed switch means, and means including switch means operable by said first cur rent responsive means for connecting said second current responsive means to the circuit when said first current responsive means is operated.

3. In a multiple station intercommunicating system, the combination including, means including interstation communication circuits, and an electroacoustical translating device, a multiposition communication controlling switch means and an amplifier having input and output connections at each station controlled by the switch means thereat enabling the device to be connected to a circuit or the amplifier input or output and the circuit to the amplifier output or input, respectively, for establishing communication circuits between stations, each station including also normally closed switch means in the circuit between said communication controlling switch means and interstation circuits, a single normally energized current responsive means,

10 means operably connecting said relay means to said normally closed switch means and operable to open the latter, means including a switch con-' amplifier is grounded and operated to open said normally closed switch means, and means including switch means operable by said, current responsive means for connecting said current re-;

sponsive means to the circuit when said means is operated.

4. A unit for an intercommunicating system including an amplifier having an input and an output, a communication circuit, means including a plural position communication direction controlling switch and amplifier input and output circuits controlled by it for controlling the connection of said circuit to the input or output of said amplifier in different positions of said switch, and means for preventing the connection of said amplifier to said communication circuit in either position of said switch under predetermined conditions of said communication circuit, said last mentioned means including a normally closed switch in said communication circuit and current responsive means connected to the circuit and controlled in response to the busy condition of said circuit operably connected to said switch for opening it.

5. A unit for an intercommunicating syste including an amplifier having an input and an output, a communication circuit, means including a plural position communication direction controlling switch and amplifier input and output circuits controlled by it for controlling the connection of said circuit to the input or output of said amplifier in different positions of said switch, and means for preventing the connection of said amplifier to said circuit in either position of said switch in the event said circuit is busy, said last mentioned means including a normally closed switch in said communication circuit, a

first current responsive means operably connected to said switch for opening it, means including a current operated busy circuit responsive means controlling the energization of said first current responsive means, and means connecting said.

busy circuit responsive means to said communication circuit.

6. A unit for an intercommunicating system including an amplifier having an input and an output, a communication circuit, means including a plural position communication direction controlling switch and amplifier input and output circuits controlled by it; means for controlling the connection of said circuit to the input or output of said amplifier in different positions of said switch, and means for preventing the connection of said amplifier to said circuit in either position of said switch under busy conditions of said circuit, said last mentioned means including a normally closed switch in said circuit, a single current responsive means operably connected to said switch means, means including switch means operable by said communication direction control switch and normally closed switch means operable by said current responsive means for. connecting said current respons ve means tosaid communication circuit, and means including other switch means operable by said current responsive means upon its operation and circuits controlled by it for. connecting said cur; rent responsive means to said conimunication circuit independently ofsaid communication die. rection controlling switch means.

'L'A unit for an intercommunicating system including an amplifier having an input and an output, a communication circuit, means include in'za plural position communication direction. controlling switch and amplifier input and out; put circuits controlled by. it for controlling the. connection of said circuit to the input or output at said amplifier in different positions at said switch, and means for preventing the. connection {it said amplifier. to. said circuit in either. position of said switch in the event said circuit is. bnsy said last mentioned means including a normally closed switch in said circuit, a single current responsive means. operablyconnected to said switch and closing said switch in one position of said current responsive. means and operable to another. position to open said switch. means including. said communication direction control-l ling switch and circuits controlled by. it for. 6011:. nesting said current responsive. means to. said communication circuit in said one position. 0% said current responsive. means thereby toirender it responsivev to a busycondition of. the. circuit, and means. including said communication direc-.. tion controlling. switch, switch means operable by. said current responsive means. and circuits controlled thereby. for connecting said current. responsive. means to. said communication circuit; in said other position of said current responsive means.

' 8. A unit for. use. in an intercommunicatina system including. an amplifier. having! an output circuit, an electnoacoustical translating; device, a communication. circuit, means-includin a com: munication direction control switch and ampli-i flea and device circuits closeable. by said: switch. ion connecting. said communication circuittdtlia output ot the. amplifier. on to said device, current responsive means? connected to said communism. circuit, and a. normallyclosed. switch in communication circuit operableibyi said 0111;; rent responsive means to open said coinmunica.-. tion circuit-,1-

sum intercommunicating unit including: a. communication circuit, electroacousticah 1118351.

latingmeansand means including a two. posi-k Q) busyl station responsive. controlmeana ton 12 connecting said translating means to said circuit in its two positions said last mentioned means including a pair of normally closed and normally open circuits and switch means in said circuits operable. by said control means for selectively completing said circuits and connecting said translators device to said commu ication circuit. said witch means. norm lly closin one, ci cuit. and rmally penin t e secon i i n one position o id; contro means. an ope n s d ne cir uit. and c os n he secon n t e other posit n o sai contr me ns. and mplifier eans co nected 21s the ci u be we aid. slatin nd; Sa nq yc os d c r- 9 ntercomme c ti e ys n l dim ne Q more stat ns Q st type an on of 9 3 t t on 9 3. econ yp l i u i lectroacoustical translating means, amplifying 20.. a, communication circuit and communi-' cat n: ont ol mea s c n i t o c ons. Qf. aid; q rcu tte said translating nd. am i ying m ans... inter a i o cir its e e said itetions, connect ible to the communication circuits as this tation esp nsiv e t e s a q o the i t. t pe. onn t o th c m ica on ir ni s. he and n udme sw tc .v m ns or. break ng,- said communication. c it an s al ns ne ones-ab e herebn i na ng. m a s a 1: t me at th second, type tor o atin ai e-- emoti means o ope ate-said gna e n nd to r a sa d comm cat o ir it wher by staiiene I he second. e an. al sa d. s ons. Q; i s ype. and co tro m an or thebusv as tation esnd is ye me ns. a s atio o e f rs is Nam s ame Dat W -,-r 3,191 531 Da is F .1 .8- ZA ZQQQ Qam bs11. Ju 33.

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t me or. r tu nin s d r sp n i me n t t nitial eond t en. o rema a c mmun on tine c rcui ans? l mm n a S n means. o ts committ e nd i a RICHARD. H. CAIMPBELL.

Refe ences Gite th fi e. of: his. na fi i i UNITED STATES PATENTS- 

